From U.S. Pat. No. 4,402,783A1, a tyre building drum is known comprising a central shaft; two coaxial cylindrical half-drums mounted to slide along the central shaft; actuating members for moving the two half-drums in opposite directions along the central shaft; and a substantially cylindrical, telescopic central body coaxial with and connecting the two half-drums. The telescopic central body comprises a tubular central member integral with an intermediate point on the central shaft; two tubular end members integral with the respective half-drums; and two tubular intermediate segments, each interposed between the tubular central member and a tubular end member.
In the above known building drum, the intermediate segments only assume a precise position with respect to the half-drums and the telescopic tubular central member when the telescopic central body is fully extended or fully contracted, but are in no way position-controlled when the telescopic central body assumes an intermediate configuration, i.e. when forming the carcass and as the half-drums return to the cycle-start position. In other words, in the above known drum, no unequivocal relationship exists between the length of the telescopic central body and the position of the intermediate segments, which poses serious drawbacks, especially when forming the carcass. When forming the carcass, in fact, the half-drums move rapidly towards each other, so that nesting of the intermediate segments is likely to result in more or less serious jamming, if all the intermediate segments are moved together.
To eliminate the above drawback and ensure that a given length of the telescopic central body corresponds unequivocally to a given position of the intermediate segments with respect to the tubular central member, the tyre building drum described in Patent EPO780220B1 has been proposed.
More specifically, the two cylindrical half-drums of the building drum described in Patent EPO780220B1 are mounted to slide on the tubular central shaft, and are moved in opposite directions along the central shaft by a central screw; and each tubular end member is supported in sliding manner by the tubular central member, and moves towards the tubular central member in opposition to the thrust exerted by a number of springs.
The building drum described in Patent EPO780220B1 eliminates the drawback described, by a given length of the telescopic central body corresponding unequivocally to a given position of the intermediate segments with respect to the tubular central member.
In the known construction solutions described above, to adapt the building drum to tyres of different widths, various parts of the telescopic central body must be replaced with like parts of a different width (i.e. different axial size). More specifically, the two tubular end members integral with the respective half-drums, and the two intermediate segments, each interposed between the tubular central member and a tubular end member, must be changed.
In the known building drums described above, changing the two tubular end members and the two intermediate segments means disassembling and removing one of the two half-drums, so as to disassemble and remove a tubular end member and the corresponding intermediate segment; and then disassembling and removing the tubular central member, so as to disassemble and remove the other tubular end member and corresponding intermediate segment. Once the old parts are removed, the new parts are assembled in reverse order: a new tubular end member, a new intermediate segment, the tubular central member, another new intermediate segment, another new tubular end member, and the half-drum.
Changing the two end members and two intermediate segments as described above are complicated, time-consuming jobs, by calling for disassembly and removal of a half-drum and the tubular central member. It is important to bear in mind that, both the half-drum and the tubular central member being too heavy (at least 50-60 kg) for manual handling, disassembly/assembly calls for use of an external lifting device (hoist or crane). Moreover, disassembling/assembling a half-drum and the tubular central member subjects the threaded parts of both to considerable mechanical wear.